According to the first explanation, the brother is reimbursed one fourth of the total. That result can be reached by saying that it is a Safek whether the brothers are Lekuchos B'achrayus (= one half reimbursement) or she'Lo b'Achrayus (= no reimbursement). If so, the Gemara had no reason to make Rav Asi's Safek broader than necessary - i.e. whether the brothers are Yorshim or Lekuchos.

According to the second explanation, in which Rav Asi entitles the brother to be reimbursed one half of the total amount that was taken from him (one fourth land and one forth money), the Gemara is clear, because the only way for Rav Asi to have reached that ruling is if he was unsure if the brothers are Yorshim or Lekuchos b'Achrayos.

D. Zupnik